1. Field of the Invention
The present invention relates to a method and an apparatus for transmitting and receiving control information in a broadcast communication system and, more particularly to a method and an apparatus for transmitting and receiving control information about a frame, which includes multiple services, in a broadcast communication system.
2. Description of the Related Art
In our 21st century information society, broadcast communication services are digitized, and multi-channel, high-quality broadband service is provided. The recent increase in the spread of high screen quality digital televisions (TVs), Portable Multimedia Players (PMPs), and portable broadcast devices has caused an increasing demand for the support of various receiving schemes in the digital broadcast service.
In order to fulfill such a demand, the Digital Video Broadcasting-Terrestrial (DVB-T2), which is a second generation European terrestrial wave digital broadcast standard, is preparing standards for a receiving scheme reusing the conventional home digital receiving antenna, a receiving scheme using multiple antennas in order to increase capacity, and a receiving scheme for a portable mobile terminal, respectively. DVB-T/H, which is a first generation terrestrial wave digital broadcast standard, takes only the two schemes including a stationary receiving scheme and a mobile receiving scheme into consideration. However, the DVB-T2 also includes a scheme of using multiple antennas, and considers a physical layer structure and a change of control information according to the physical layer structure as a main standardization job.
In the physical layer structure of the DVB-T2, a control channel is a channel for transmitting a control message with respect to a transmission scheme in the physical layer. In the control channel, a basic unit of a transmitted signal is a frame, which may include multiple services, and includes a service index, location information, a modulation scheme/coding rate, and a cell identifier (ID) of each service. In the control channel, the service configuration and related information may be different according to each frame. Therefore, for each frame, the control channel is transmitted separately from the data channel.
Referring to FIG. 1, a transmitter 102 transmits different broadcast services in multiple Radio Frequency (RF) bands, respectively, and a receiver 104 tunes to an RF containing a desired service and receives the desired service. For example, when the receiver 104 wants to receive the service 1, the receiver 104 tunes to RF #1, obtains information, such as location information and modulation/coding scheme, relating to the service 1, and then decodes the service 1.
Referring to FIG. 2A, the transmitter 202 divides a service (corresponding to each service in FIG. 1), which includes an existing long packet configured by combining multiple RFs, into multiple short sub-slots, and then transmits the divided sub-slots through multiple RF bands. The receiver 204 detects the location of a pertinent service in each RF band including a desired service through the control information and then receives the pertinent service. In receiving the service 1, the receiver 204 decodes the pertinent services in an order capable of receiving the sub-slots in the time domain, i.e., in the order of RF1, RF4, RF3, and RF2. Therefore, for the same quantity of service, transmission of a smaller quantity of data through multiple frequencies is expected to be capable of achieving more time and frequency diversity gains than simultaneous transmission of a large quantity of data by using a fixed RF for each service. Such a frame configuration scheme as described above is called Time-Frequency Slicing (TFS).
In the structure shown in FIG. 2B, ten service packets are transmitted through four RFs. In such a TFS frame, all service packets are first allocated to one RF, and packets cyclic-shifted from the initial group of all the service packets are then allocated to an adjacent RF. When four RF bands are used as shown in FIG. 2B, one service is transmitted through four RFs (RF1˜RF4). Therefore, each service basically includes four sub-slots. However, as in the service 3, the service may include five sub-slots due to the cyclic shift.
Referring to FIG. 2B, a P1 signal 201 and a P2 signal 203 are transmitted at the initial portion of each frame. The P1 signal 201 may be used as a preamble for synchronization, and the P2 signal 203 transmits control information for each service included in the current or next frame. The control information includes location information indicating the start point and the terminating point of data of each service. When the receiver switches the service channel while receiving the service, the receiver can receive the switched service only after acquiring the control information of the switched service.
FIG. 3 illustrates conventional service switching. When multiple frames (frame n, . . . , frame n+3) are being transmitted in the time domain, each frame includes a P2 signal 303 to 311 at the initial portion thereof and multiple services following the P2 signal. The frame may be transmitted in the FF mode or TFS mode, as shown in FIG. 1 or 2. However, for convenience of description, transmission in the FF mode will be taken into consideration in the following description. Further, for convenience of description, it is assumed that the P2 signal indicates control information of the current frame.
Referring to FIG. 3, when the receiver switches the channel to another service while receiving a service at frame n (301), the receiver decodes the P2 signal for receiving the switched service at the next frame. Since the P2 signal 305 includes the scheduling information at frame (n+1), the receiver is unable to receive the switched service at frame (n+1) if the receiver fails to decode the P2 signal 305. Further, if the receiver continuously fails to decode the P2 signal, that is, if the receiver fails to decode not only the P2 signal 305 but also the P2 signal 307 of frame (n+2), the receiver receives the switched service at frame (n+3) by using the control information 313 acquired from the P2 signal 309 of frame (n+3).
According to the conventional systems described above, when a service switching occurs, the zapping time from the time point of the service switching to the time point of reception of the switched service may be too long according to whether the decoding of the P2 signal is a success or failure. Therefore, there has been a request for a scheme for transmitting and receiving control information of switched service so that the receiver can efficiently receive the switched service when a service switching has occurred.